The subject matter disclosed herein relates to switching devices using optical input, and more specifically to hardening the mechanical motion of a micro electromechanical systems (MEMS) device from electromagnetic interference.
Electronic switches are typically employed for the purpose of varying an electrical circuit between conducting states. Some switches, especially those with high impedance drive circuits, can be inadvertently activated with electro magnetic (EM) interference. For example, EM interference can couple onto switch drive logic connections, which are typically high input impedance circuits, and cause spurious switching logic transients. The switching logic transients, in turn, cause unintended switch activation. Some approaches to avoid the production of spurious switching logic transients include filtering the switch drive logic lines to mitigate EM interference coupling using L-C or R-C networks. However, some switches, such as micro electromechanical system (MEMS)-based switches, may operate at high frequencies such that conventional filtering technologies may not be able to operate at sufficient rates to be useful in MEMS applications. One example of such a system in which a switch may experience EM interference is a magnetic resonance imaging (MRI) system.
In MRI systems, a highly uniform, static magnetic field is produced by a primary magnet to align the spins of gyromagnetic nuclei within a subject of interest (e.g., hydrogen in water/fats). The nuclear spins are perturbed by a radiofrequency (RF) transmit pulse, encoded based on their position using gradient coils, and allowed to equilibrate. During equilibration, faint RF fields are emitted by the spinning, processing nuclei and are detected by a series of RF coils. The signals resulting from the detection of the RF fields are then processed to reconstruct a useful image.
The MRI system may include features to prevent damage to certain of the RF coils, such as those that receive faint RF signals from within a patient, while the RF transmit pulse and/or gradient pulses are being performed. Typically, blocking signals are provided to the receiving coils to prevent resonance with the RF transmit and gradient pulses, which can result in eddy currents, heat production, image artifacts, and potential damage to various electrical components. However, as noted above, some high impedance drive circuits employed in conjunction with switches that allow the blocking signals to be provided to the coils can experience spurious switching logic transients. The transients may result in the receiving coil being converted to a resonant state, which can be undesirable during certain phases of operation of the MRI system. Accordingly, a need exists for improved EM-hardened techniques for switching electrical circuits, such as those present in MRI systems.